Novel radiation sensitive compounds and radiation sensitive compositions containing the same

ABSTRACT

Pyrylium, thiapyrylium and selenapyrylium salts and derivatives thereof having a trimethine linkage containing an aryl substituent attached to at least one carbon atom of the trimethine linkage are disclosed. Radiation sensitive compositions, e.g., photoconductive compositions, containing such materials are also disclosed.

This is a division of application Ser. No. 813,371, filed July 6, 1977,now U.S. Pat. No. 4,173,473.

FIELD OF THE INVENTION

This invention relates to new organic radiation sensitive compoundsuseful, for example, in photoconductive compositions.

BACKGROUND OF THE INVENTION

The process of xerography, as disclosed by Carlson in U.S. Pat. No.2,297,691, employs an electrophotographic element comprising a supportmaterial bearing a coating of a normally insulating material whoseelectrical resistance varies with the amount of incident actinicradiation it receives during an imagewise exposure. The element,commonly termed a photoconductive element, is first given a uniformsurface charge after a suitable period of dark adaptation. The elementis then exposed to a pattern of actinic radiation which has the effectof differentially reducing the potential of the surface charge inaccordance with the relative energy contained in various parts of theradiation pattern. The differential surface charge or electrostaticlatent image remaining on the electrophotographic element is then madevisible by contacting the surface with a suitable electroscopic markingmaterial. Such marking material or toner, whether contained in aninsulating liquid or on a dry carrier, can be deposited on the exposedsurface in accordance with either the charge pattern or in the absenceof charge pattern as desired. The deposited marking material can then beeither permanently fixed to the surface of the sensitive element byknown means such as heat, pressure, solvent vapor and the like ortransferred to a second element to which it may similarly be fixed.Likewise, the electrostatic latent image can be transferred to a secondelement and developed there.

Various photoconductive insulating materials have been employed in themanufacture of electrophotographic elements. For example, vapors ofselenium and vapors of selenium alloys deposited on a suitable supportand particles of photoconductive zinc oxide held in a resinous,film-forming binder have found wide application in present-day documentcopying applications.

Since the introduction of electrophotography, a great many organiccompounds have been found to possess some degree of photoconductivity.Many organic compounds such as poly(vinyl carbazole) have revealed auseful level of photoconduction and have been incorporated intophotoconductive compositions. Optically clear organicphotoconductor-containing elements having desirable electrophotographicproperties can be especially useful in electrophotography. Suchelectrophotographic elements may be exposed through a transparent base,if desired, thereby providing unusual flexibility in equipment design.Such compositions when coated as a film or layer on a suitable supportalso yield an element which is reusable; that is, it can be used to formsubsequent images after residual toner from prior images has beenremoved by transfer and/or cleaning.

Although many of the organic photoconductor materials are inherentlylight sensitive, their degree of sensitivity is usually low so that itis often necessary to add materials to increase their speed. Increasingthe electrophotographic speed has several advantages in that it reducesexposure time, allows projection printing through various opticalsystems, etc. By increasing the speed through the use of sensitizers,photoconductors which would otherwise have been unsatisfactory areuseful in processes where higher speeds are required. Accordingly, thereis a need for new materials useful as sensitizers of organicphotoconductor-containing systems.

Pyrylium salts, as disclosed in Davis et al, U.S. Pat. No. 3,141,770issued July 21, 1964 and in VanAllan et al, U.S. Pat. No. 3,250,615issued May 10, 1966, have been found to be useful sensitizing compoundsfor photoconductive compositions, especially organic photoconductivecompositions. Since the initial discoveries of Davis et al and VanAllanat al as set forth in the above-referred to patents, a variety of newindividual species of pyrylium salts, as well as thiapyrylium andselenapyrylium salts, have been discovered and found to be useful asradiation sensitive addenda in photoconductive compositions as well asin other radiation sensitive compositions such as laser Q-swtiches andvarious types of filter elements such as infrared absorbing filterelements. For example, Reynolds and VanAllan in U.S. Pat. No. 3,417,083issued Dec. 17, 1968 disclose the use of certain new stable polymethinepyrylium and thiapyrylium salts useful as laser Q-switches and asinfrared absorbing dyes useful in various filter applications. Inaddition to the various polymethine pyrylium and thiapyrylium dyestructures shown in U.S. Pat. No. 3,417,083, Reynolds et al in U.S. Pat.No. 3,938,994 issued Feb. 17, 1976 discloses the use of certainmonomethine pyrylium and thiapyrylium salts useful as sensitizers in anorganic photoconductive composition.

Because of the especially useful properties which have been found to beassociated with various pyrylium, thiapyrylium, and selenapyryliumsalts, much work has been done pertaining to the synthesis of pyryliumsalts to discover further new and useful species of these materials. Inthis regard, for background purposes, reference may be made to thosespecies of pyrylium salts disclosed, for example, in Contois et al, U.S.Pat. No. 3,586,500 issued June 22, 1971 and in Contois U.S. Pat. No.3,577,235 issued May 4, 1971. Still other species of pyrylium saltswhich have been found to be useful as sensitizers for low-colorphotoconductive compositions are disclosed in VanAllan, U.S. Pat. No.3,554,745 issued Jan. 12, 1971. Still other species of pyrylium saltmaterials are disclosed in Defensive Publications T889,021; T889,022;and T889,023; all issued on Aug. 31, 1971. Yet other useful species ofpyrylium salt materials are disclosed in Belgium Pat. No. 754,066 datedSept. 30, 1970 and in Reynolds et al, U.S. patent application Ser. No.60,634 filed Aug. 3, 1970 and now abandoned.

SUMMARY OF THE INVENTION

In accord with the present invention there are provided novel pyrylium,thiapyrylium, and selenapyrylium salts and derivatives thereof,hereinafter referred to as pyrylium-type salts, which contain atrimethine linkage having an aryl substituent bonded to at least one ofthe carbon atoms of the trimethine linkage. These materials andradiation sensitive compositions containing the same unexpectedlyexhibit advantageous and superior properties when compared to closelyrelated pyrylium-type salts absent such an aryl substituent in thetrimethine linkage thereof.

For example, the novel pyrylium salts of the present invention, whenincorporated in photoconductive compositions, have been found tounexpectedly yield substantially higher photosensitivity than closelyrelated trimethine-containing pyrylium salts; and these same novelpyrylium salts have also been found to advantageously exhibit low visualcoloration so that they are useful in radiation sensitive compositionswherein low color components are required, e.g., as sensitizers for usein (a) substantially colorless, transparent organic photoconductivecompositions and (b) photoconductive coated paper elements wherein theresultant coated paper material is desired to have the color andappearance of plain paper (bond paper).

In addition, the novel salts of the present invention exhibit lightabsorption properties extending into the infrared portion of thespectrum so that these compositions may be used in a variety ofdifferent radiation sensitive elements requiring infrared absorbing,radiation sensitive addenda.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Representative pyrylium-type salts of our invention have, or representan equivalent of a material having, a structure of the followingformula: ##STR1## wherein: each of X¹ and X², which may be the same ordifferent, represent oxygen, sulfur, or selenium;

each of Y¹ and Y², which may be the same or different, represent theatoms necessary to complete a substituted or unsubstituted heterocyclicunsaturated ring nucleus having 6 or 10 ring atoms including a selenium,sulfur or oxygen hetero ring atom and 5 or 9 carbon ring atoms;

each of R¹, R², and R³, which may be the same or different, representhydrogen, halogen such as chlorine or bromine, cyano, nitro, substitutedor unsubstituted alkyl having 1 to about 4 carbon atoms in the alkylgroup, or substituted or unsubstituted aryl, e.g., phenyl andalkoxyphenyl, with the proviso that at least one of R¹, R², or R³represents substituted or unsubstituted aryl; and

Z.sup.⊖ represents an anionic function such as a perchlorate,fluoroborate, or hexafluoroborate anion.

A partial listing of representative substituent groups which may bepresent in the case where any one of R¹ -R³ represents a substitutedaryl includes alkyl and alkoxy groups having 1 to about 4 carbon atoms;amino groups including alkyl- and phenyl-substituted amino groups suchas dialkylaminos wherein the alkyl substituents of such amino groupscontain 1 to about 4 carbon atoms, dibenzylaminos, diphenylaminos,ditolylaminos; and equivalent aryl substituents.

A partial listing of representative substituent groups which may bepresent in the case where any one of R¹ -R³ represents a substitutedalkyl includes phenyl groups, alkoxy and amino groups as defined above,and equivalent alkyl substituents.

In accord with certain preferred embodiments of the invention, each ofR¹ -R³ in Formula I, which may be the same or different, representhydrogen, alkyl having 1 to 4 carbon atoms, phenyl or alkoxyphenyl, atleast one of R¹ -R³ being phenyl or alkoxyphenyl; and the heterocyclicrings containing Y¹ in formula I above represent groups having either offormulas II or III and the heterocyclic rings containing Y² in formula Irepresent groups having either of formulas IV or V: ##STR2## wherein:each of X¹ and X², which may be the same or different, represent oxygenor sulfur;

Z is as defined above; and

each of R⁴, R⁵, R⁶, R⁷, R⁸, and R⁹, which may be the same or different,represent hydrogen; alkyl having 1 to about 4 carbon atoms in the alkylgroup, including alkyls substituted with an alkoxy having 1 to about 4carbon atoms, an amino substituent of the type defined hereinabove withrespect to R¹ -R³, or phenyl; substituted or unsubstituted aryl asdefined hereinabove with respect to R¹ -R³ ; and when taken together anytwo R⁴ -R⁹ groups attached to adjacent carbon ring atoms represent theatoms necessary to complete substituted or unsubstituted aryl as definedhereinabove with respect to R¹ -R³.

Although the heterocyclic structures of formulas II-V above presentlyrepresent preferred embodiments of the pyrylium-type salts of theinvention, it should be understood that a variety of equivalentstructures are also contemplated within the scope of the presentinvention. Among the various references to which one may refer forfurther information regarding such heterocyclic structures are thevarious United States patents and Defensive Publications referred to inthe "Background of the Invention". It is to be understood that ofprimary importance in the present invention is the presence of thearomatic substituent on the trimethine linkage.

The pyrylium salts described herein can be prepared by one of thegeneral reaction sequences described hereinafter. The thiapyrylium andselenapyrylium analogs of these salts can be prepared by similartechniques, except that in these cases the hetero oxygen atom appearingin the pyrylium or flavylium salt starting materials are replaced by asulfur or selenium hetero atom, respectively. According to one generalreaction scheme, symmetrical salts are conveniently prepared as follows:##STR3## wherein R² is as defined hereinbefore.

Various substituted pyrylium salts bearing substituents represented bygroups R⁴ -R⁶ and R⁷ -R⁹ in formulas II-V above can be prepared inaccord with reaction scheme VI by utilizing appropriately substitutedstarting materials. For example, symmetrical pyranylidene salts areconveniently prepared from either 1 or 4-methylflavylium salts asillustrated in reaction scheme VII: ##STR4## wherein R² is as definedhereinbefore.

Unsymmetrical pyrylium salts can be prepared by the condensation of a4-arylacylidenepyran with a 2- or 4-methylflavylium salt or with a 2- or4-methyl substituted pyrylium salt in the presence of acetic anhydrideas illustrated in reaction schemes VIII and IX respectively. ##STR5##wherein R² and R⁴ -R⁷, are as defined hereinbefore. ##STR6## wherein R²,R⁴ -R⁶, and R⁷ -R⁹ are as defined hereinbefore.

Where it is desired to prepare pyrylium salts of the present inventionhaving substituents on the α or γ position of the trimethine linkage,rather than the β position of the linkage as illustrated in reactionschemes VI-IX above, this can be accomplished by reacting aformylmethylenepyran derivative and a 4-alkylpyrylium in refluxing1,2,3-trichloropropane as illustrated in reaction scheme X: ##STR7##wherein R¹, R³, R⁴ -R⁶, and R⁷ -R⁹ are as defined hereinbefore.

Photoconductive compositions and electrophotographic elements containingthe same can be prepared with a variety of organic and inorganicphotoconductive materials together with the pyrylium-type saltsdescribed herein. Typically, in such photoconductive compositions thepyrylium-type salts described herein are present as sensitizers. Suchphotoconductive compositions can be prepared by blending a dispersion orsolution of the photoconductive compound together with an electricallyinsulating, film-forming resin binder when necessary or desirable andcoating or forming a self-supporting layer with the photoconductivecomposition. Generally, a suitable amount of the sensitizing compound ismixed with the photoconductive coating composition so that afterthorough mixing, the sensitizing compound is uniformly distributedthroughout the desired layer of the coated element. The amount ofsensitizer that can be added to a photoconductor-containing layer togive effective increases in speed can vary widely. The optimumconcentration in any given case will vary with the specificphotoconductor and sensitizing compound used.

In general, an appropriate sensitizer is added in a concentration rangefrom about 0.0001 to about 30 percent by weight based on the dry weightof the film-forming coating composition. Normally, the sensitizer isadded to the coating composition in an amount from about 0.005 to about10 percent by weight of the total coating composition.

The sensitizers used in this invention are effective for enhancing theelectrophotosensitivity of a wide variety of organic and inorganicphotoconductors, particularly organic, including organo-metallicphotoconductors. A partial listing of representative organicphotoconductors useful in photosensitive compositions containing thepresent sensitizers is set forth below.

1. Arylamine photoconductors including substituted and unsubstitutedarylamines, diarylamines, nonpolymeric triarylamines and polymerictriarylamines such as those described in Fox, U.S. Pat. No. 3,240,597,issued Mar. 15, 1966 and Klupfel et al., U.S. Pat. No. 3,180,730, issuedApr. 27, 1965;

2. Polyarylalkane photoconductors of the types described in Noe et al.U.S. Pat. No. 3,274,000, issued Sept. 20, 1966, Wilson U.S. Pat. No.3,542,547, issued Nov. 24, 1970 and in Seus et al., U.S. Pat. No.3,542,544, issued Nov. 24, 1970;

3. 4-Diarylamino-substituted chalcones of the types described in FoxU.S. Pat. No. 3,526,501, issued Sept. 1, 1970;

4. Non-ionic cycloheptenyl compounds of the types described in LookerU.S. Pat. No. 3,533,786, issued Oct. 13, 1970;

5. Compounds containing an

    >N--N<

nucleus, as described in Fox U.S. Pat. No. 3,542,546, issued Nov. 24,1970;

6. Organic compounds having a 3,3'-bis-aryl-2-pyrazoline nucleus, asdescribed in Fox et al. U.S. Pat. No. 3,527,602, issued Sept. 8, 1970;

7. Triarylamines in which at least one of the aryl radicals issubstituted by either a vinyl radical or a vinylene radical having atleast one active hydrogen-containing group, as described in Brantly etal. U.S. Pat. No. 3,567,450, issued Mar. 2, 1971;

8. Triarylamines in which at least one of the aryl radicals issubstituted by an active hydrogen-containing group, as described inBrantly et al. Belgian Pat. No. 728,563, dated Apr. 30, 1969;

9. Any other organic compound which exhibits photoconductive propertiessuch as those set forth in Australian Pat. No. 248,402 and the variouspolymeric photoconductors such as the photoconductive carbazol polymersdescribed in U.S. Pat. No. 3,421,891, dated Jan. 14, 1969.

Preferred binders for use in preparing the photoconductive layers whichcan be sensitized in accordance with the method of this inventioncomprise polymers having fairly high dielectric strength which are goodelectrically insulating film-forming vehicles. Materials of this typecomprise styrenebutadiene copolymers; silicone resins; styrene-alkydresins; silicone alkyd resins; soya-alkyd resins; poly(vinyl chloride);poly(vinylidene chloride); vinylidene chloride-acrylonitrile copolymers;poly(vinyl acetate); vinyl acetate-vinyl chloride copolymers; poly(vinylacetals), such as poly(vinyl butyral); polyacrylic and methacrylicesters, such as poly(methylmethacrylate), poly(n-butylmethacrylate),poly(isobutyl methacrylate), etc.; polystyrene; nitrated polystyrene;polymethylstyrene; isobutylene polymers; polyesters, such aspoly(ethylene alkaryloxyalkylene terephthalate); phenolformaldehyderesins; ketone resins; polyamides; polycarbonates; polythiocarbonates;poly(ethyleneglycol-co-bishydroxyethoxyphenylpropane terephthalate);nuclear substituted polyvinyl haloarylates; etc. Methods of makingresins of this type have been described in the prior art, for example,styrene-alkyd resins can be prepared according to the method describedin U.S. Pat. Nos. 2,361,019 and 2,258,423. Suitable resins of the typecontemplated for use in the photoconductive layers of the invention aresold under such tradenames or trademarks as Vitel® PE-101, Cymac,Piccopale 100, Saran F-220 and Lexan® 105 and 145. Other types ofbinders which can be used in the photoconductive layers of the inventioninclude such materials as paraffin, mineral waxes, etc. If a polymericphotoconductor is used, the binder may be omitted altogether.

The organic coating solvents useful for preparing the above coatingdopes can be selected from a variety of materials. Useful liquids arehydrocarbon solvents, including substituted hydrocarbon solvents, withpreferred materials being halogenated hydrocarbon solvents. Therequisite properties of the solvent are that it be capable of dissolvingthe pyrylium dye and capable of dissolving or at least highly swellingor solubilizing the polymeric ingredient of the composition. Inaddition, it is helpful if the solvent is volatile, preferably having aboiling point of less than about 200° C. Particularly useful solventsinclude halogenated lower alkanes having from 1 to about 3 carbon atoms,such as dichloromethane, dichloroethane, dichloropropane,trichloromethane, trichloroethane, tribromomethane,trichloromonofluoromethane, trichlorotrifluoroethane, etc.; aromatichydrocarbons such as benzene, toluene as well as halogenated benzenecompounds such as chlorobenzene, bromobenzene, dichlorobenzene, etc.;ketones such as dialkyl ketones having 1 to about 3 carbon atoms in thealkyl moiety such as dimethylketone, methylethylketone, etc.; and etherssuch as tetrahydrofuran, etc. Mixtures of these and other solvents canalso be used.

In preparing the photoconductive coating composition, useful results areobtained where the photoconductor substance is present in an amountequal to at least about 1 weight percent based on the dry weight of thecoating composition. The upper limit in the amount of photoconductorsubstance present can be widely varied in accordance with usualpractice. In those cases where a binder is employed, it is normallyrequired that the photoconductor substance be present in an amount fromabout 1 weight percent of the coating composition to about 99 weightpercent of the coating composition. A polymeric photoconductor can beemployed in which case an additional binder may not be required. Apreferred weight range for the photoconductor substance in the coatingcomposition is from about 10 weight percent to about 60 weight percent.

Suitable supporting materials for coating photoconductive layers whichcan be sensitized in accordance with the method of this invention caninclude any of a wide variety of electrically conducting supports, forexample, paper (at a relative humidity above 20 percent); aluminum-paperlaminates; metal foils such as aluminum foil, zinc foil, etc.; metalplates, such as aluminum, copper, zinc, brass and galvanized plates;vapor deposited metal layers such as silver, nickel, aluminum and thelike coated on paper or conventional photographic film bases such ascellulose acetate, polystyrene, etc. Such conducting materials as nickelcan be vacuum deposited on transparent film supports in sufficientlythin layers to allow electrophotographic elements prepared therewith tobe exposed from either side of such elements. An especially usefulconducting support can be prepared by coating a support material such aspoly(ethylene terephthalate) with a conducting layer containing asemiconductor dispersed in a resin. Such conducting layers both with andwithout insulating barrier layers are described in U.S. Pat. No.3,245,833. Likewise, a suitable conducting coating can be prepared fromthe sodium salt of a carboxyester lactone of maleic anhydride and avinyl acetate polymer. Such kinds of conducting layers and methods fortheir optimum preparation and use are disclosed in U.S. Pat. No.3,007,901 and 3,262,807.

Coating thicknesses of the photoconductive composition on the supportcan vary widely. Normally, a coating in the range of about 10 microns toabout 300 microns before drying is useful for the practice of thisinvention. The preferred range of coating thickness is found to be inthe range from about 50 microns to about 150 microns before drying,although useful results can be obtained outside of this range. Theresultant dry thickness of the coating is preferably between about 1micron and about 50 microns, although useful results can be obtainedwith a dry coating thickness between about 0.5 and about 200 microns.

The elements of the present invention can be employed in any of thewell-known electrophotographic processes which require photoconductivelayers. One such process is the xerographic process as described, forexample, in the "Background of the Invention" set forth herein and inU.S. Pat. No. 3,938,994 referred to hereinbefore.

As indicated earlier herein, the pyrylium-type salts of the inventioncan be useful as a radiation sensitive material in a variety ofradiation sensitive compositions and elements. One preferred embodimentof such radiation sensitive compositions is illustrated by thephotoconductive compositions described hereinbefore. However, thepyrylium-type salts of the invention can also be used in radiationsensitive elements other than the aforementioned photoconductorelements. In this connection, the pyrylium-type salts of the inventionare regarded as particularly useful radiation sensitive addenda becauseof their advantageous properties of low visible coloration combined withgood transmittance of visible light radiation and unusually highabsorptivity and sensitivity to radiation in the far red and nearinfrared portions of the electromagnetic spectrum, herein defined asradiation having a wavelength greater than about 680 nm. For example,the pyrylium-type salts of the invention can be incorporated in variousthermographic compositions and elements as a radiation sensitivematerial sensitive to infrared or heat radiation. In such applications,the radiation sensitive pyrylium-type salts of the invention can beapplied as a layer to a support, preferably together with a carriermaterial for the salt, such as a binder, and other necessary ordesireable radiation sensitive or image-forming materials.

In addition, the pyrylium-type salts of the invention can be used as aradiation sensitive filter composition and element to filter out orremove undesired infrared radiation. In such case, a simple layercontaining the pyrylium-type salts of the invention (and optionally abinder) or a solution or dispersion of the pyrylium-type salt in aliquid carrier can be employed as an effective radiation sensitivefilter composition or element in accord with the invention.

As will be appreciated, the various carrier materials such as bindersand liquids optionally employed in radiation sensitive compositionstogether with the pyrylium-type salts of the invention can be selectedfrom among a wide variety of materials which do not substantially impairthe radiation sensitivity and absorption properties of the pyrylium-typesalts of the invention, i.e., the carrier material is a"non-interfering" carrier. A partial listing of useful such carrierswould include any of the electrically insulating binders described foruse hereinbefore in photoconductive compositions as well as manyconventional photographic silver halide vehicles including variouscolloid materials containing gelatin, gelatin derivatives or a varietyof other hydrophilic naturally-occurring and synthetic substances suchas those described in Product Licensing Index, Vol. 92, December, 1971,publication 9232, page 108, paragraph VIII. (The publication ProductLicensing Index is published by Industrial Opportunities Ltd., Homewell,Havant, Hampshire, P09 1EF, United Kingdom.)

The following examples are included for a further understanding of theinvention.

EXAMPLE 1--Preparation of4-[3-(2,6-Diphenyl-4H-pyran-4-ylidene)-2-phenylpropen-1-yl]-2,6-diphenylpyryliumperchlorate having the formula: ##STR8## where φ represents --C₆ H₅,i.e., a phenyl group.

A mixture of 5 g. of 4-methyl-2,6-diphenylpyrylium perchlorate, 10 ml.of acetonitrile, 10 ml. of benzoyl chloride and 5 ml. of pyridine wasrefluxed for 5 minutes, cooled and the solid was collected and extractedin a Soxhlet extractor with acetonitrile. The resultant product wasidentified as the above-noted pyrylium salt having a melting point of303°-304° C. and an empirical formula of C₄₃ H₃₁ ClO₆.

EXAMPLE 2--Preparation of4-[3-(2,6-Diphenyl-4H-pyran-4-ylidene)-2-phenylpropen-1-yl]flavyliumperchlorate having the formula: ##STR9##

A mixture of 1 g. 2,6-diphenyl-4-phenacylidene-4H-pyran, 1.3 g. of4-methylflavylium perchlorate and 20 ml. of acetic anhydride wasrefluxed for 15 minutes, chilled and the solid was collected andpurified by extraction. The resultant product had a melting point of299°-300° C. and was identified as the above-noted pyrylium salt havingan empirical formula of C₄₁ H₂₉ ClO₆.

EXAMPLE 3--Preparation of4-[3-(4H-Benzopyran-4-ylidene)2-phenylpropen-1-yl]flavylium perchloratehaving the formula: ##STR10##

This pyrylium salt was made in a manner identical to that set forth inExample 1 above, except the pyrylium perchlorate salt starting materialof Example 1 was replaced with 4-methylflavylium perchlorate. Thepyrylium salt product was identified as the above-noted salt having amelting point of 298°-299° C. and an empirical formula of C₃₉ H₂₇ ClO₆.

EXAMPLE 4--Preparation of4-[3-(2,6-Diphenyl-4H-pyran-4-ylidene)-2-(p-methoxyphenyl)propen-1-yl]-2,6-diphenylpyryliumperchlorate having the formula: ##STR11##

This pyrylium salt was prepared in a manner identical to that set forthin Example 1 above, except that benzoyl chloride used in Example 1 wasreplaced by p-anisoyl chloride. The resultant product was identified asthe above-noted pyrylium salt having a m.p. of 312°-313° C. and anempirical formula of C₄₄ H₃₃ ClO₇.

EXAMPLE 5

The electronic absorption spectra of each of the four pyrylium saltsprepared in Examples 1-4 was measured in methylene chloride using a Cary14 spectrometer. The long wavelength absorption band, b, for each ofthese salts was as follows:

    ______________________________________                                                              b                                                       ______________________________________                                        Pyrylium salt of Example 1                                                                            690 nm.                                               Pyrylium salt of Example 2                                                                            704 nm.                                               Pyrylium salt of Example 3                                                                            728 nm.                                               Pyrylium salt of Example 4                                                                            693 nm.                                               ______________________________________                                    

EXAMPLE 6

A series of photoconductive compositions containing one of the followingphotoconductors:

A. triphenylamine

B. 4,4'-bis(diethylamino)-2,2'-dimethyltriphenylmethane

C. 4,4'-bis(diphenylamino)chalcone

as the photoconductive material was prepared for coating on a conductingsupport material by mixing 0.25 part of the photoconductor with 0.01part by weight of one of the following compounds:

1.4-[3-(2,6-Diphenyl-4H-pyran-4-ylidene)-2-phenylpropen-1-yl]-2,6-diphenylpyryliumperchlorate

2. 4-[3-(2,6-Diphenyl-4H-pyran-4-ylidene)-2-phenylpropen-1-yl]flavyliumperchlorate

3. 4-[3-(4H-Benzopyran-4-ylidene)-2-phenylpropen-1-yl]flavinyliumperchlorate

4.4-[3-(2,6-Diphenyl-4H-pyran-4-ylidene)-2-(p-methoxyphenyl)-propen-1-yl]-2,6-diphenylpyryliumperchlorate

as sensitizer and dissolving the mixture, together with 1.0 part byweight of a resinous polyester binder, by stirring the mix intodichloromethane. The resultant mixture was then hand coated over apolymeric carboxy ester lactone layer carried on a transparent support.In all instances, the polyester binder in the coating composition wasVitel PE-101 (trademark of Goodyear Tire and Rubber Co.), believed to bepoly(4,4'-isopropylidenebisphenoxyethylene-co-ethylene terephthalate)50/50. The wet coating thickness on the support was 0.01 cm. Afterdrying, a sample of each electrophotographic element was employed in astandard electrophotographic process which includes charging under apositive corona discharge until the surface potential of the sample, asmeasured by an electrometer probe, reached 600 volts. Similarly, asample of each element was charged under a negative source until thesurface potential reached 600 volts. Each of the samples was thenexposed from behind a transparent stepped density gray scale to a 3000°K. tungsten source of 20 foot-candle illuminance at the point ofexposure. The exposure caused reduction of surface potential of theelement under each step of the gray scale from its initial potential,V_(o), to some lower potential, V, the exact value of which depends uponthe actual amount of exposure received by each area. The results ofthese measurements were then plotted on a graph of surface potential Vversus log exposure for each step. The actual speed of each element wasexpressed in terms of the reciprocal of the exposure required to reducethe surface potential to any fixed arbitrarily assigned value.Numerically, the shoulder speeds noted below are the quotient of 10⁴divided by the exposure in meter candle seconds required to reduce thepotential by 100 volts. The toe speeds noted below are the quotient of10⁴ divided by the exposure in meter-candle-seconds required to reducethe initial voltage, V_(o), to an absolute value of 100 volts. Theresults of these speed measurements are given in the following table.

                  TABLE I                                                         ______________________________________                                                       Speed                                                          Compound                                                                              Organic      Positive    Negative                                     Number  Photoconductor                                                                             Shoulder Toe  Shoulder                                                                             Toe                                 ______________________________________                                        1       A             900     50    630   25                                  2       A             900     57    900   32                                          B            1000     63   1200   40                                          C            1600     80   1000   45                                  3       A            1200     50    800   25                                          B            1000     57    900   29                                          C             900     57    450   40                                  4       A            1200     45   1000   18                                          B            1200     63   1600   32                                          C            1400     63   1000   25                                  ______________________________________                                    

For comparison, photoconductors A, B and C employed in thephotoconductive compositions used to obtain the data shown in Table Iare evaluated in samples containing no sensitizer. The speeds are asfollows:

                  TABLE II                                                        ______________________________________                                                  Speed                                                               Organic     Positive        Negative                                          Photoconductor                                                                            Shoulder   Toe      Shoulder                                                                              Toe                                   ______________________________________                                        A           44         0        52      0                                     B           19         0        18      0                                     C           101        0        32      0                                     ______________________________________                                    

As an additional basis for comparison, pyrylium salts having atrimethine linkage and which are otherwise structurally similar tocompounds 1-4 above, except that they do not possess an aryl substituentattached to a carbon atom of the methine linkage, were evaluated assensitizers with photoconductors A, B, and C noted above. Theseevaluations were carried out by preparing photoconductive compositionsand making speed measurements on the resultant photoconductivecompositions in a manner identical to that described above. Theresulting speed values obtained are set forth in Table III as follows:

                  TABLE III                                                       ______________________________________                                        Pyrylium                                                                      Salt                 Speed                                                    Compound Organic     Positive    Negative                                     Tested.sup.1                                                                           Photoconductor                                                                            Shoulder Toe  Shoulder                                                                             Toe                                 ______________________________________                                        i        A           29       0    20     0                                            B           220      10   140    9                                   ii       A           32       0    40     0                                            B           570      29   450    25                                           C           120      12   110    9                                   iii      A           36       0    36     0                                            B           100      4.5  100    4.0                                          C           63       0    70     5.0                                 iv       A           100      3.2  71     2.5                                          B           160      5.0  120    4.0                                          C           160      8.0  120    5.0                                 v        A           52       3.5  80     3.0                                          B           280      13   500    12                                           C           130      3.0  63     --                                  vi       A           120      0    250    0                                            B           200      5.6  58     6.3                                          C           120      0    120    0                                   vii      A           50       0    32     0                                            B           250      18   360    11                                           C           70       3.6  90     0                                   viii     A           200      16   180    6.3                                          B           400      32   250    18                                           C           630      55   400    25                                  ______________________________________                                         .sup.1 See following page.                                               

Compound i has the chemical name4-[1,3-dimethyl-3-(2,6-diphenyl-4H-pyran-4-ylidene)propen-1-yl]-2,6-diphenylpyryliumperchlorate and the following structural formula: ##STR12## Compound iihas the chemical name4-[2-methyl-3-(2,6-diphenyl-4H-pyran-4-ylidene)propen-1-yl]-2,6-diphenylpyryliumperchlorate and the following structural formula: ##STR13## Compound iiihas the chemical4-[3-(4H-benzopyran-4-ylidene)-2-ethylpropen-1-yl]flavylium perchlorateand the following structural formula: ##STR14## Compound iv has thechemical name4-[2-ethyl-3-(2,6-diphenyl-4H-pyran-4-ylidene)propen-1-yl]-2,6-diphenylpyryliumperchlorate and the following structural formula: ##STR15## Compound vhas the chemical name4-[3-(2,6-diphenyl-4H-pyran-4-ylidene)propen-1-yl]-2,6-diphenylpyryliumperchlorate and the following structural formula: ##STR16## Compound vihas the chemical name4-[3-(4H-benzopyran-4-ylidene)-2-methylpropen-1-yl]flavylium perchlorateand the following structural formula: ##STR17## Compound vii has thechemical name4-[3-methyl-3-(2,6-diphenyl-4H-pyran-4-ylidene)propen-1-yl]-2,6-diphenylpyryliumperchlorate and the following structural formula: ##STR18## Compoundviii has the chemical name2,6-di-t-butyl-4-[3-2,6-di-t-butyl-4H-pyran-4-ylidene)propen-1-yl]pyryliumperchlorate and the following structural formula: ##STR19##

As can be seen by comparing Table I to Table III, the pyrylium salts ofthe present invention which have a trimethine linkage bearing an arylsubstituent can be used in photoconductive compositions to impartthereto significantly higher speeds, i.e., light sensitivity, than canbe imparted to identical compositions using structurally similarpyrylium salts, except that these latter salts do not possess an arylsubstituent on the trimethine linkage thereof.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

We claim:
 1. A pyrylium-type salt having the formula: ##STR20## wherein:each of X¹ and X², which may be the same or different, representsoxygen, sulfur, or selenium;each of Y¹ and Y², which may be the same ordifferent, represents the atoms necessary to complete a heterocyclicunsaturated ring nucleus having 6 or 10 ring atoms including a selenium,sulfur or oxygen hetero ring atom and 5 or 9 carbon ring atoms; each ofR¹, R², and R³, which may be the same or different, represents hydrogen,halogen, cyano, nitro, alkyl having 1 to about 4 carbon atoms in thealkyl group, or aryl, with the proviso that at least one of R¹, R², orR³ represents phenyl or alkoxyphenyl; and Z.sup.⊖ represents an anionicfunction.
 2. A pyrylium-type salt as described in claim 1 wherein:eachof R¹ -R³, which may be the same or different, represents hydrogen,alkyl, phenyl or alkoxyphenyl; the heterocyclic ring containing Y¹represents a group having one of the following structures: ##STR21## andwherein the heterocyclic ring containing Y² represents a group havingone of the following structures: ##STR22## wherein each of X¹ and X²,which may be the same or different, represents oxygen or sulfur;Zrepresents an anionic function; and each of R⁴, R⁵, R⁶, R⁷, R⁸, and R⁹,which may be the same or different, represents hydrogen, alkyl having 1to 4 carbon atoms in the alkyl group, phenyl, and when taken togetherany two R⁴ -R⁹ groups attached to adjacent carbon ring atoms representthe atoms necessary to complete an aryl ring.
 3. A pyrylium-type saltselected from the group consisting of4-[3-(2,6-Diphenyl-4H-pyran-4-ylidene)-2-phenylpropen-1-yl]-2,6-diphenylpyryliumperchlorate;4-[3-(2,6-Diphenyl-4H-pyran-4-ylidene)-2-phenylpropen-1-yl]flavyliumperchlorate;4-[3-(4H-Benzopyran-4-ylidene)-2-phenylpropen-1-yl]flavyliumperchlorate; and4-[3-(2,6-Diphenyl-4H-pyran-4-ylidene)-2-(p-methoxyphenyl)propen-1-yl]-2,6-diphenylpyryliumperchlorate.
 4. A radiation sensitive composition comprising a radiationsensitive material which absorbs radiation having a wavelength ofgreater than about 680 nm., said material having the formula: ##STR23##wherein: each of X¹ and X², which may be the same or different,represents oxygen, sulfur, or selenium;each of Y¹ and Y², which may bethe same or different, represents the atoms necessary to complete aheterocyclic unsaturated ring nucleus having 6 or 10 ring atomsincluding a selenium, sulfur or oxygen hereto ring atom and 5 or 9carbon ring atoms; each of R¹, R², and R³, which may be the same ordifferent, represents hydrogen, halogen, cyano, nitro, alkyl having 1 toabout 4 carbon atoms in the alkyl group, or aryl, with the proviso thatat least one of R¹, R², or R³ represents phenyl or alkoxyphenyl; andZ.sup.⊖ represents an anionic function.
 5. A radiation sensitivecomposition comprising a radiation sensitive pyrylium-type salt and anon-interfering carrier for said salt, said salt having the formula:##STR24## wherein: each of X¹ and X², which may be the same ordifferent, represents oxygen, sulfur, or selenium;each of Y¹ and Y²,which may be the same or different, represents the atoms necessary tocomplete a heterocyclic unsaturated ring nucleus having 6 or 10 ringatoms including a selenium, sulfur or oxygen hetero ring atom and 5 or 9carbon ring atoms; each of R¹, R², and R³, which may be the same ordifferent, represents hydrogen, halogen, cyano, nitro, alkyl having 1 toabout 4 carbon atoms in the alkyl group, or aryl, with the proviso thatat least one of R¹, R², or R³ represents aryl; and Z.sup.⊖ represents ananionic function.
 6. A radiation sensitive composition as defined inclaim 5 wherein said composition comprises said radiation sensitivematerial admixed in a non-interfering liquid or in a non-interferingbinder.
 7. A radiation sensitive composition as defined in claim 5wherein:each of R¹ -R³, which may be the same or different, representhydrogen, alkyl, phenyl or alkoxyphenyl; the heterocyclic ringcontaining Y¹ represents a group having one of the following structures:##STR25## and wherein the heterocyclic ring containing Y² represents agroup having one of the following structures: ##STR26## wherein each ofX¹ and X², which may be the same or different, represents oxygen orsulfur;Z represents an anionic function; and each of R⁴, R⁵, R⁶, R⁷, R⁸,and R⁹, which may be the same or different, represents hydrogen, alkylhaving 1 to 4 carbon atoms in the alkyl group, phenyl, and when takentogether any two R⁴ -R⁹ groups attached to adjacent carbon ring atomsrepresent the atoms necessary to complete an aryl ring.
 8. A radiationsensitive composition as defined in claim 5 wherein said pyrylium-typesalt is selected from the group consisting of4-[3-(2,6-Diphenyl-4H-pyran-4-ylidene)-2-phenylpropen-1-yl]-2,6-diphenylpyryliumperchlorate;4-[3-(2,6-Diphenyl-4H-pyran-4-ylidene)-2-phenylpropen-1-yl]flavyliumperchlorate;4-[3-(4H-Benzopyran-4-ylidene)-2-phenylpropen-1-yl]flavyliumperchlorate; and4-[3-(2,6-Diphenyl-4H-pyran-4-ylidene)-2-(p-methoxyphenyl)propen-1-yl]-2,6-diphenylpyryliumperchlorate.